edac: x38 fix mchbar high register addr

Intel X38 MCHBAR is a 64bits register, base from 0x48, so its higher base
is 0x4C.

Signed-off-by: Lu Zhihe <tombowfly@gmail.com>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Cc: <stable@kernel.org>		[2.6.30.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>